garage sale GT

If you have a large tire and a small tire and they both deform the same percent, then the volume of rubber undergoing hysteresis is larger in the large tire. Same shape change, greater size.

SquidPuppet

Exactly correct. That's why I said ~15%. That's also why I said extreme variations like 3% vs 30% wouldn't be fair.

This brings us full circle so I'll quote myself.

^ That is an obvious exaggeration, and maybe close to a 3% vs 30% comparison. It's unfair, but it makes the point than an eqaulity can be found somwhere in between.

We both know we are not going to ride the small tire all mushy (massive rolling resistance) at 60psi, and we wouldn't ride the big tire inflated to (unnecessary) granite status. Where does that leave us? If we determined the perfect desired amount of energy required to roll the tire and defined it as "rolling resistance X", we would be able to achieve that with either tire by fine tuning pressure, but ultimately the large tire would require less. The result is the same rolling resistance, but better ride quality with the large tire. That's why I say that for noncompetetive cruising applications, nobody will notice a speed difference, but they will notice a bump absorbing difference.

I can't say I remember the exact number, but 14.83 MPH is stuck in my head for some reason as the threshold over which greater tire width started to suck up energy due to air drag. So folks interested recreational speedy riding would certainly benifit from narrow tires, and that's what I'd recommend.

garage sale GT

You seem to think deformation percent and rolling resistance are the same. They are not. If the tire is larger and deforms the same percent, it is deforming more rubber.
The narrower tire can withstand a greater percentage of deformation than the wider tire to have the same rolling resistance. it will have the same rolling resistance at 20 or 25% as the wide one will at 15%

It will probably still be at a higher PSI.

The ride just doesn't get that bad with a narrow tire at high PSI because it can deform easier than a wide one at high pressure, especially over lengthwise cracks or bumps.

SquidPuppet

No no. We agree on that. Thay are connected, but not the same.

Agreed. Thats why I said ~15%. Meaning "give or take" a very small amount.

If we are still comparing a 35mm to a 50mm tire it will be far less extreme. If a 35mm tire is at 15% deformation, I'd wager the 50mm tire would need to be at ~13% to achieve the same rolling resistance. We are only talking about 2.25mms deformational difference at 15%.

Yes. And in the 35 vs 50 scenario, it would be significantly greater. I weigh 165lbs and the 50mm Kojak is a solid pice of granite at 50psi. The 35 is noticably cushy at 80.

Confused on that one. Why would the wide tire be at a high pressure? It needn't be.

surreal

Hey Squidley.... I'd throw in the towel on this one. He's right; skinnier 26"s will make your bike lightning-quick. From what I understand, GSGT regularly wins Cat 1 races on his cruiser, rolling 35mm Kojaks.

SquidPuppet

But, but, but... I frequently win Cat 1 races on Bontrager Hanks.... 2.2s.

/

surreal

I've been doing pretty well on rollerskates.... not winning, but top ten finishes. They're not the plushest ride, but punctures haven't been a problem.

SquidPuppet

Plushness? Puncture resistance? Meh, let's get to the core issue. How's the rolling resistance on 'em?




Oh, and when I say Cat 1, I'm serious. And the cat is usually arthritic or weak sighted, or both. But I smoke him more often than he beats me.

surreal

Ha....

The skates roll pretty good, but I'm thinking I might switch from 62mm to 650b, if they'll clear the skates' undercarriage. I think the larger diameter will be tremendously helpful offroad-- I use my skates for road races and XC as well.

1FJEF

I think a Fuji Cape May has 25mm wide rims. How much do you weigh? Perhaps look here.